In Boston, hospitals are restricting visitors to protect patients with weakened immune systems; some are barring children under 14 years altogether from traipsing through their wards. And hospital personnel are carefully …

Last fall, 162 harbor seal pups mysteriously washed up dead on the shores of New Hampshire and Massachusetts. Puzzled, scientists conducted autopsies on five of the animals, which suggested that a respiratory infection had killed …

The H1N1 flu pandemic of 2009-10 killed an estimated 284,500 people, according to Centers for Disease Control and Prevention (CDC) scientists — an estimate that is 15 times higher than the previously recorded official death toll.